CHEYENNE - A hydrothermal explosion sent a towering column of boiling water, mud, and rock shooting into the air at Yellowstone National Park in Wyoming on July 23 morning, destroying a section of boardwalk and sending dozens of tourists running for safety, officials said.

No injuries were reported, according to the United States Geological Survey, but the area remained closed to the public.

The explosion occurred around 10am (midnight on July 24 Singapore time) in the Biscuit Basin area of the park.

Several tourists captured video of the event, and in some footage an adult can be heard shouting at children to run.

The explosion was a couple of miles north of the Old Faithful Geyser, which regularly shoots steam into the sky.

“This is quite a bit different than Old Faithful,” said Dr Michael Poland, the scientist in charge at the Yellowstone Volcano Observatory, who said the hydrothermal event took place near Black Diamond Pool in Biscuit Basin.

Explosions like the one on July 23 happen when water suddenly turns to steam in the underground “plumbing” beneath the park’s hydrothermal system, Dr Poland said.

The change can be caused by a major event like an earthquake. “That’s not the case here,” he said. “Instead, what we had was a very localised change in this plumbing system. Pressure can build, and you can get an explosion like this.”

Similar explosions took place in the Norris Geyser Basin this year and at Biscuit Basin in 2009.

In a statement, US Geological Survey officials assured that the episode was not connected to a change in volcanic activity, either. (Yes, Yellowstone a...